LECTURE ONE The Astronomy of Climate

Transcription

1 LECTURE ONE The Astronomy of Climate

2 Agricultural Science Climatology Semester 2, 2006 Richard Thompson Course Coordinator: Mike Wheatland

3 AMMENDED TIMETABLE SUMMARY The following table summarises the activities associated with the unit for the semester. Items are labelled as follows: Lecture (L), Workshop (W), Web Activity (Web), and Laboratory (Lab). Day Date Topic Week 5 (of semester) L1 Mon 20 Aug Weather and Climate (Ch. 1) W1 Tues 21 Aug Electrical Safety L2 Thur 23 Aug The Earth and Sun 1 (Ch. 2) Week 6 L3 Mon 27 Aug The Earth and Sun 2 (Ch. 2) W2 Tues 28 Aug Radiation and the Environment L4 Thur 30 Aug Our Atmosphere and Electromagnetic Radiation (Ch. 3) Week 7 Web 1 Mon 3 Sep No formal lecture Web Activity 1 (due 11 Sep) Circulation Systems W3 Tues 4 Sep Global Warming and the Greenhouse Effect L5 Thur 6 Sep Water in our Atmosphere (Ch. 4) Week 8 L6 Mon 10 Sep Weather and Storms (Ch. 5) Web 2 Tues 11 Sep No formal workshop - Web Activity 2 (due 18 Sep) El Nino and the Southern Oscillation Index Web Activity 1 to be submitted to Student Support Office L7 Thur 13 Sep Climate Change and Global Warming Week 9 L8 Mon 17 Sep Balance in Nature (Ch. 6) W4 Tues 18 Sep Synoptic (Weather) Charts Web Activity 2 to be submitted during this Workshop L9 Thur 20 Sep Properties of water (Ch. 7) Lab 1 Fri 21 Sep Expt 1 (Teams 01 to 06) Expt 2 (Teams 07 to 12) Expt 3 (Teams 13 to 18) Expt 4 (Teams 19 to 24) Week 10 Web 3 Mon 1 Oct No formal lecture Web Activity 3 (due 9 Oct) Transfer Processes W5 Tues 2 Oct Plant Micro-environments L10 Thur 4 Oct Materials: Elasticity & Viscosity (Ch. 7, 8) Lab 2 Fri 5 Oct Expt 2 (Teams 01 to 06) Expt 3 (Teams 07 to 12) Expt 4 (Teams 13 to 18) Expt 1 (Teams 19 to 24)

4 Week 11 L11 Mon 8 Oct Materials: Elasticity & Viscosity (Ch. 7, 8) W6 Tues 9 Oct Life in a Fluid Web Activity 3 to be submitted during this Workshop Web 4 Thur 11 Oct No formal lecture Web Activity 4 (due 16 Oct) Fluids in and around us Lab 3 Fri 12 Oct Expt 3 (Teams 01 to 06) Expt 4 (Teams 07 to 12) Expt 1 (Teams 13 to 18) Expt 2 (Teams 19 to 24) Week 12 L12 Mon 15 Oct Farm Machinery: Friction and Lubrication (Ch. 9) W7 Tues 16 Oct Soil Moisture Web Activity 4 to be submitted during this Workshop Web 5 Thur 18 Oct No formal lecture Web Activity 5 Farm Machinery - Vibrations Lab 4 Fri 19 Oct Expt 4 (Teams 01 to 06) Expt 1 (Teams 07 to 12) Expt 2 (Teams 13 to 18) Expt 3 (Teams 19 to 24) Week 13 L13 Mon 22 Oct Farm Machinery: Stability (Ch. 10) W8 Tues 23 Oct Examination Practice L14 Thur 25 Oct Farm Structures & Machinery: Vibrations (Ch. 11)

5 Course Goals Evaluate & interpret information, based on scientific arguments Understand the physical principles relevant to your field of study Use scientific terminology correctly Be able to appreciate the analysis essential to developing a model of the physical environment

6 Preparation for Workshops Students should read Workshop Notes before Class Marks are awarded for Group Contribution at the end of the Workshop: 0 to 5 marks Teams of 3 students for Workshops & 6 for some Lab Classes - must know team number e.g. 1A 1B, 13A 13B, 23A 23B Workshops held in Second Year Laboratory in School of Physics - sit at a space where there is an A3 sheet marked with team number for the team mind map. Make sure that your name and SID are recorded on the worksheet

7 Mind ( Link ) Maps Visual summary of content of Workshop Notes List scientific terms (include units for physical quantities) on far left of A3 sheet List physical principles, laws, definitions, equations, maths, graphs, etc on the left of the A3 sheet Use colour, pictures, or diagrams to emphasize key ideas and concepts Collect relating information into "boxes Indicate how ideas are linked together Summarize notes with minimum words (no padding words "e.g.", "a", "the", "when", etc)

8 Example of a Mind Map

9 Example of a Mind Map (2) Source: Christine Lindstrom

10 Web Based Activities Activity 1 due on 11 September (Physics Student Office) Activity 2 due on 18 September (At Workshop W4) Activity 3 due on 9 October (At Workshop W6) Activity 4 due on 16 October (At Workshop W7) Activity 5 not assessed Remember that material from the web activities may be included in the examination

11 SI System of Units distance - metres m time - seconds s speed - m.s -1 energy - joules J power - watts W intensity - W.m -2 mass kg temperature - kelvin K Other units: Energy - kilowatt hours kw.h (1 kw.h = 3.6x10 6 J) Time - hours h Power - kilowatts kw (1000 W = 1 kw) Prefixes: nano micro milli kilo k mega giga G n μ m M

12 Scientific Notation (1) Many numbers are either too big, too small, or not known with enough precision to be written out in full. Physics and other sciences use scientific notation (powers of 10) for numbers and values are written in a form such as: 1.99 x kg (mass of the sun); 9.46x10 12 km (distance light travels in a year) Use appropriate number of significant figures

13 Climatology Lectures L1: Weather and Climate ( Astronomy of Climate ) L2: The Earth and Sun ( The Physics of Climate ) L3: The Earth and Sun ( More Physics of Climate ) L4: Our Atmosphere (Structure of the Atmosphere) L5: Water in our Atmosphere L6: Weather and Storms L7: Climate Change and Global Warming

14 Chapter 1 Weather, Climate and Agriculture Weather and climate are fundamental to agriculture. Both are driven by radiation from the sun and depend on a variety of astronomy (such as the seasons) and physics. It is important to have an understanding of these processes.

15 Weather & Climate Climate long-term patterns in the air surrounding us. Weather daily variations in temperature, rainfall, air pressure, humidity, wind. Climates change on different time-scales. Principle drivers of weather water in the atmosphere and radiation from the sun. Many drivers of climate including solar variations, vegetation and evolution, life itself, arrangement of continents

16 Climate for Alice Springs in July Mean daily maximum temperature - deg C 19.6 Mean no. of days where Max Temp >= 40.0 deg C 0 Mean no. of days where Max Temp >= 35.0 deg C 0 Mean no. of days where Max Temp >= 30.0 deg C 0 Highest daily Max Temp - deg C 31.6 Mean daily minimum temperature - deg C 4 Mean no. of days where Min Temp <= 2.0 deg C 12.5 Mean no. of days where Min Temp <= 0.0 deg C 6 Lowest daily Min Temp - deg C -7.5 Mean monthly rainfall - mm 14 Median (5th decile) monthly rainfall - mm 2.6 9th decile of monthly rainfall - mm st decile of monthly rainfall - mm 0 Mean no. of raindays 2.6 Highest monthly rainfall - mm 144 Lowest monthly rainfall - mm 0 Highest recorded daily rainfall - mm 76.8 Mean no. of clear days 21.4 Mean no. of cloudy days 4.2 Mean daily hours of sunshine 9.1 Highest recorded wind gust - km/h 90.7 Mean daily evaporation - mm 3.9

17 Weather Map for July 13, 2006

18 Earth and Sun

19 Earth s Place in the Solar System Sun source of radiation and solar wind. Seasons due to tilted Earth revolving about the Sun, not variation in distance. Variation in light & warming over the year. How does the Sun move during the year? Electromagnetic spectrum not uniform transmission through the atmosphere.

20 The Sun in Ultraviolet Light

21 Layers of the Sun

22 Solar System from Space Source: NASA Simulator

23 The Planets of the Solar System Source: NASA (not pictured Pluto)

24 Earth s Orbit Around the Sun Parameter Value Sidereal Period Aphelion (Jul 7 th in 2007) Perihelion (Jan 3 rd in days x 10 6 km x 10 6 km Ellipticity Inclination of Orbit Reference value (but 7.25 with respect to Solar Equator

25 Earth Orbit Question 1. How much bigger does the sun appear at perihelion than at aphelion? 2. How much larger apparent area does the sun have at perihelion than at aphelion? 3. Does this have any effect on weather and climate

26 Answers (1) 1. Angular size (θ) = Real Diameter (D) / Distance (d). Therefore: θ a = D / d a and θ p = D / d p θ p / θ a = d a / d p = / = Sun appears 3.4 % large in angular size at perihelion 2. Apparent area is proportional to θ 2 and hence ratio of apparent areas varies as : [θ p / θ a ] 2 = [d a / d p ] 2 = Sun appears 6.9 % larger in area at perihelion

27 Answers (2) 3. Effect on weather is likely to be insignificant as orbital variation is relatively small. Effect on climate also likely to be small as variation is small and rapid (only over a year) BUT Earth s orbit varies (due to pull of planets, especially Jupiter). Perihelion can occur at other times of year. Need positive feedback in climate system but orbital variations do appear in climate record (Ice Ages and Milanovitch Cycles).

28 The Seasons (1)

29 The Earth at Different Seasons Wikipedia

30 Source: Wikipedia The Seasons (2)

31 Source: Wikipedia The Seasons (3)

32 Daylight Region (Northern Summer Solstice)

33 Daylight Region (Equinox)

34 Daylight Region (Southern Summer Solstice)

35 Co-ordinate System for Stars

36 Solar Declination through the Year

37 Astronomical Seasons (1) Solar Declination curve has four special points: Equinoxes: Occurs twice per year when solar declination is zero (approx March 21 and September 21). The sun is then directly above the earth s equator. The sun rises due east everywhere on earth. Likewise, it sets due west for everywhere on earth. Well not quite!! At the poles at equinox, the sun does not rise or set at all but traverses around the horizon.

38 Astronomical Seasons (2) Solstices: The declination of the sun reaches an extreme value (±23.5 degrees) twice per year. Winter solstice is approx December 21. Summer solstice is approx June 21. Astronomers have a northern hemisphere bias!! At winter solstice, the sun is directly overhead at latitude 23.5 degrees South. This is the Tropic of Capricorn (where does this name come from??)

39 Astronomical Seasons (3) At summer solstice the sun is directly overhead at latitude 23.5 degrees North. This latitude is called the Tropic of Cancer (where does this name come from??) North of latitude = 66.5 degrees North, the sun is visible for 24 hours per day (called circumpolar). This latitude is called the (northern) polar circle. South of latitude = 66.5 degrees South the sun is not visible at all over the day. This latitude is the (southern) polar circle.

40 Astronomical Seasons (4) As well as moving in declination (latitude) the sun moves in longitude (called right ascension) relative to the background stars. At the March (Vernal) Equinox) the sun is/was in the star constellation of Aries (the Ram). At summer solstice it is in the constellation of Cancer (the Crab). Hence the name of the Tropic.

41 Zenith Distance / Altitude of Sun Sydney at Noon Southern latitude declination Winter Solstice ( = 58.5 deg / 31.5 deg) Equinox (35 + 0) = 35 deg / 55 deg) Summer Solstice ( ) = 11.5 deg / 78.5 deg)

42 Zenith Distance / Altitude of Sun Mawson (Antarctica) at Noon Southern latitude declination Winter Solstice ( = 91 deg / -1.0 deg) Equinox ( = 67.5 deg / 22.5 deg) Summer Solstice ( = 44 deg / 56 deg)

43 Dates for the Astronomical Seasons UTC Date and Time of Solstice and Equinox year Equinox Mar Solstice June Equinox Sept Solstice Dec day time day time day time day time : : : : : : : : : : : : : : : : : : : : : : : : : : : :38

44 Seasons in Australia Start Middle End Summer December 01 mid January February 28/29 Autumn March 01 mid April May 31 Winter June 01 mid July August 31 Spring September 01 mid October November 30

45 Temperature Lag 30 Temperature Variations for Sydney Summer Solstice Mean Maximum Temperature Winter Solstice 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month

46 Length of Day (Southern Hemisphere) Length of Day - Sunrise to Sunset Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec

47 Angular Variation of Intensity Summer sun is high in the sky at noon f A S θ θ A G A G = A S /cos θ Winter Sun is low in the sky at noon

48 Angular Variation of Intensity (2) Zenith Angle (θ) for 1000 Watts m -2 incident intensity Altitude Cos (θ) Intensity Wm

49 Solar Insolation (1) Solar insolation is the total energy received per unit area Insolation depends the average elevation angle of the sun during the day and is there also related to the length of the day For any location on earth this depends on season and latitude The sun tends to be at a lower elevation angle at high latitudes but this is offset by the longer day length during the summer season

50 Solar Insolation (2)

51 Solar Insolation (3) Insolation at the equator does not vary greatly throughout the year Yearly variation of insolation becomes larger as we go to higher latitudes. At summer solstice insolation actually increases as we move to higher latitudes. This is because the increased length of the day offsets the lower average altitude of the sun

52 Refraction in the Atmosphere REFRACTION of sunlight by the Earth s Atmosphere Sunset horizon - apparant position of Sun Sunrise actual position of Sun atmosphere

53 An Extreme Case of Refraction